The JET machine uses a variety of current transducers for control and protection of the plasma, the coils and their associated power supplies. This paper reviews the various measuring technologies, within the range 5­100kA, used on JET to assist with the selection of high-current transducers for future plasma control/tokamak applications; these include Rogowski coils, Coaxial Shunts, Hall-effect transducers, zero-flux CTs and a Faraday-effect optical transducer. The paper considers cost, reliability, accuracy and usability based on up to thirty years of operational experience of the transducers. Accuracy of the magnet current measurements is important in the control of tokamak plasmas and there has been considerable effort to improve it. Recently a Faraday-effect optical current sensor has been used to measure up to 67kA in the Toroidal Field (TF) coil circuit. This measurement system has been calibrated at JET to verify its 0.1% accuracy. In addition the data acquisition system for this measurement is automatically calibrated at the start of each JET pulse. The improved accuracy has been shown to enhance the spatial consistency of kinetic profiles at JET. Due to its portability the JET project intends to employ the same Faraday-effect current transducer to calibrate other high current transducers by temporarily fitting it to other busbars; such as those in the Ohmic Heating network.